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    Home Unlabelled Hardware support: PSA: Performance Doesn't Scale Linearly With Wattage (aka testing M1 versus a Zen 3 5600X at the same Power Draw)

    Hardware support: PSA: Performance Doesn't Scale Linearly With Wattage (aka testing M1 versus a Zen 3 5600X at the same Power Draw)

    November 30, 2020

    Hardware support: PSA: Performance Doesn't Scale Linearly With Wattage (aka testing M1 versus a Zen 3 5600X at the same Power Draw)

    PSA: Performance Doesn't Scale Linearly With Wattage (aka testing M1 versus a Zen 3 5600X at the same Power Draw)

    Posted: 29 Nov 2020 02:19 PM PST

    Alright, so all over the internet - and this sub in particular - there is a lot of talk about how the M1 is 3-4x the perf/watt of Intel / AMD CPUs.

    That is true... to an extent. And the reason I bring this up is that besides the obvious mistaken examples people use (e.g. comparing a M1 drawing 3.8W per CPU core against a 105W 5950X in Cinebench is misleading, since said 5950X is drawing only 6-12W per CPU core in single-core), there is a lack of understanding how wattage and frequency scale.

    (Putting on my EE hat I got rid of decades ago...)

    So I got my Macbook Air M1 8C/8C two days ago, and am still setting it up. However, I finished my SFF build a week ago and have the latest hardware in it, so I thought I'd illustrate this point using it and benchmarks from reviewers online.

    Configuration:

    • Case: Dan A4 SFX (7.2L case)
    • CPU: AMD Ryzen 5 5600X
    • Motherboard: ASUS B550I Strix ITX
    • GPU: NVIDIA RTX 3080 Founder's Edition
    • CPU Cooler: Noctua LH-9a Chromax
    • PSU: Corsair SF750 Platinum

    So one of the great things AMD did with the Ryzen series is allowing users to control a LOT about how the CPU runs via the UEFI. I was able to change the CPU current telemetry setting to get accurate CPU power readings (i.e. zero power deviation) for this test.

    And as SFF users are familiar, tweaking the settings to optimize it for each unique build is vital. For instance, you can undervolt the RTX 3080 and draw 10-20% less power for only small single digit % decreases in performance.

    I'm going to compare Cinebench R23 from Anandtech here in the Mac mini. The author, Andrei Frumusanu, got a single-thread score of 1522 with the M1.

    In his twitter thread, he writes about the per-core power draw:

    5.4W in SPEC 511.povray ST

    3.8W in R23 ST (!!!!!)

    So 3.8W in R23ST for 1522 score. Very impressive. Especially so since this is 3.8W at package during single-core - it runs at 3.490 for the P-cluster

    So here is the 5600X running bone stock on Cinebench R23 with stock settings in the UEFI (besides correcting power deviation). The only software I am using are Cinebench R23, HWinfo64, and Process Lasso which locks the CPU to a single core (so it doesn't bounce core to core - in my case, I locked it to Core 5):

    Power Draw

    Score

    End result? My weak 5600X (I lost the silicon lottery... womp womp) scored 1513 at ~11.8W of CPU power draw. This is at 1.31V with a clock of 4.64 GHz.

    So Anandtech's M1 at 1522 with a 3.490W power draw would suggest that their M1 is performing at 3.4x the perf/watt per core. Right in line with what people are saying...

    But let's take a look at what happens if we lock the frequency of the CPU and don't allow it to boost. Here, I locked the 5600X to the base clock of 3.7 GHz and let the CPU regulate its own voltage:

    Power Draw

    Score

    So that's right... by eliminating boost, the CPU runs at 3.7 GHz at 1.1V... resulting in a power draw of ~5.64W. It scored 1201 on CB23 ST.

    This is case in point of power and performance not scaling linearly: I cut clocks by 25% and my CPU auto-regulated itself to draw 48% of its previous power!

    So if we calculate perf/watt now, we see that the M1 is 26.7% faster at ~60% of the power draw.

    In other words, perf/watt is now ~2.05x in favor of the M1.

    But wait... what if we set the power draw of the Zen 3 core to as close to the same wattage as the M1?

    I lowered the voltage to 0.950 and ran stability tests. Here are the CB23 results:

    Power Draw

    Scores

    So that's right, with the voltage set to roughly the M1 (in my case, 3.7W) and a score of 1202, we see that wattage dropped even further with no difference in score. Mind you, this is without tweaking it further to optimize how low I can draw the voltage - I picked an easy round number and ran tests.

    End result?

    The M1 performs at, again, +26.7% the speed of the 5600X at 94% the power draw. Or in terms of perf/watt, the difference is now 1.34 in favor of the M1.

    Shocking how different things look when we optimize the AMD CPU for power draw, right? A 1.34 perf/watt in favor of the M1 is still impressive, with the caveat that the M1 is on TSMC 5nm while the AMD CPU is on 7nm, and that we don't have exact core power draw (P-cluster is drawing 3.49W total in single-CPU bench, unsure how much the other idle cores are drawing when idling)

    Moreover, it shows the importance of Apple's keen ability to optimize the hell out of its hardware and software - one of the benefits of controlling everything. Apple can optimize the M1 to the three chassis it is currently in - the MBA, MBP, and Mac mini - and can thus set their hardware to much more precise and tighter tolerances that AMD and Intel can only dream of doing. And their uarch clearly optimizes power savings by strongly idling cores not in use, or using efficiency cores when required.

    TL;DR: Apple has an impressive piece of hardware and their optimizations show. However, the 3-4x numbers people are spreading don't quite tell the whole picture, because performance (frequencies, mainly), don't scale linearly. Reduce the power draw of a Zen 3 CPU core to the same as an M1 CPU core, and the perf/watt gap narrows to as little as 1.23x in favor of the M1.

    edit: formatting

    edit 2: fixed number w/ regard to p-cluster

    edit 3: Here's the same CPU running at 3.9 GHz at 0.950V drawing an average of ~3.5W during a 30min CB23 ST run:

    Power Draw @ 3.9 GHz

    Score

    submitted by /u/nice_big_cup_of_stfu
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